Myasthenia gravis (MG)

Overview

Myasthenia gravis (MG) is a long-term autoimmune condition causing 'fatigable' muscle weakness — weakness that builds with repeated use and eases with rest — most often affecting the eye muscles first. It's more common in women than men; symptoms typically start before 40 in women and after 60 in men, though MG can affect any age. Severity and which muscles are affected both vary a lot between people, but MG is usually manageable with medication and supportive care.

Symptoms

Symptoms fluctuate through the day, often worse by evening, and can be triggered or worsened by heat, infections, stress, or a menstrual period. MG can stay limited to the eyes (ocular myasthenia) or spread more widely (generalised myasthenia gravis).

The eyes are usually affected first — drooping eyelids and blurred or double vision, both of which can change from day to day and often worsen later in the day. Facial, mouth and throat weakness can make expressions harder to form, affect speech (sometimes slurred or nasal-sounding), and make chewing and swallowing difficult, which carries a risk of choking, aspiration and chest infections. In generalised MG, weakness can extend to the neck (making it hard to hold the head up), arms (difficulty lifting them above the shoulders) and legs (harder to walk far or climb stairs, with a higher fall risk). Fatigue — a deeper tiredness than muscle weakness alone — is common even when the condition is otherwise well controlled.

Cause

Some people are more prone to autoimmune conditions generally because of small inherited variations across many genes, though MG itself isn't considered directly hereditary. Most people with MG produce antibodies against the acetylcholine receptor (AChR), a protein at the neuromuscular junction where nerve signals reach muscle; these antibodies block the receptor and interfere with that signal. A smaller group instead produce antibodies against muscle-specific kinase (MuSK), which disrupts the same communication by a different route. Rarer antibodies (such as LRP4) turn up in some people, and a proportion have no detectable antibodies at all ('seronegative' MG). In some cases the thymus gland appears to play a role in triggering the abnormal immune response.

Getting a diagnosis

A GP refers to a neurologist, who combines a physical exam and history with a blood test for the relevant antibodies — though some people, particularly with ocular MG, don't show high antibody levels initially, and the test may need repeating if symptoms persist. Nerve and muscle electrical testing, plus a CT or MRI scan of the chest to check the thymus gland, round out the diagnostic picture.

Management and outlook

Care works best through a multidisciplinary team, usually led by a neurologist at a specialist neuromuscular clinic. Avoiding known triggers where possible — stress, fatigue, infections, certain medications and anaesthetics — helps, and the pneumococcal vaccine plus an annual flu jab are recommended.

Medication options include pyridostigmine (often tried first, helping nerve signals reach the muscle more effectively), steroids like prednisolone to calm the immune response, other immunosuppressants (azathioprine, methotrexate, mycophenolate, rituximab), and newer targeted treatments (efgartigimod, rozanolixizumab, zilucoplan). Thymectomy (surgical removal of the thymus) is recommended for anyone with a thymoma, and for some younger patients with AChR antibodies and recent-onset disease even without a thymoma — it can improve symptoms and reduce the medication needed, though it doesn't help people with MuSK antibodies.

A sudden, severe worsening (myasthenic crisis, with extreme weakness and breathing or swallowing difficulty) is a medical emergency needing hospital treatment — usually plasma exchange or IV immunoglobulin alongside steroids. Around 1 in 5 people have 'refractory' MG, where standard treatments don't fully control symptoms. Pregnancy needs careful planning with a neuromuscular team well in advance, to keep both mother and baby safe through pregnancy and delivery.